The present invention relates to graphics plotters and, more particularly, in a graphics plotter having a driving roller mechanism for moving a writing medium over a platen disposed adjacent the roller mechanism and having a generally horizontal table portion and a curved outer portion where the writing medium is smoothly curved from a generally horizontal supported state to an unsupported vertically hanging state, to the method of improving the platen to eliminate static charge buildup problems comprising horizontally grooving the upper surface of at least the curved outer portion of the platen at spaced intervals to create a plurality of horizontal grooves of substantially V-shaped cross-section so as to create, in effect, a series of overlapped plates on the surface of the platen, covering the surface of the platen with a uniform layer of a static charge conducting material, and splattering the surface of the platen with additional static charge conducting material of a sufficiently viscous consistency so as to create a series of slightly raised conductive bumps on the surface of the platen on which a writing medium can be supported and over which it can ride.
Graphics plotters constructed with a drive system as shown in simplified form in FIG. 1 have become very popular because of their ability to handle large sheets of paper or other writing mediums in a small floor space. As shown in end view in FIGS. 1-3, there is a driving roller 10 over which the writing medium 12 is moved by being pinched between the driving roller 10 and a plurality of pinch rollers 14 as the driving roller 10 is reversably driven in one direction and then the other. To support the writing medium 12 for smooth movement back and forth and to provide a supported surface for drawing upon the writing medium 12 as it is moved, there are a pair of platens 16 disposed with one on each side of the rollers 10, 14. The platens 16 each have a generally horizontal table portion 18 and a curved outer portion 20 where the writing medium is smoothly curved from a generally horizontal supported state to an unsupported vertically hanging state.
With slow plotting speeds, the foregoing prior art configuration was suitable for its purpose; that is, the writing medium 12 moved back and forth without problem.. With the introduction of faster and faster plotting speeds, however, physical distortion of the writing medium such as that depicted in FIG. 3 began to create serious problems. As depicted in FIG. 2, as the writing medium 12 is pulled over a platen 16 from the vertical to the horizontal, there is no problem. Such is not the case on the other side of the rollers 10, 14, however, where the writing medium 12 is being pushed from its horizontal state on the table portion 18 over the curved outer portion 20 as depicted in FIG. 3. The static charges built up on the writing medium 12 (particularly with thin vellums, and the like) as a result of the dragging motion across the platens 16 cause it to cling and stick to the surface of the platen 16 which, in turn, causes it to bunch up and move erratically, causing associated problems. Coating the surface of the platens 16 with a static charge conductive material as is known in the art provides some relief; but, not complete relief.
Wherefore, it is the object of the present invention to provide a platen for use in such pinch roller driven graphics plotters, and the like, wherein static charge clinging of the writing medium is virtually eliminated.
Other objects and benefits of the present invention will become apparent from the description which follows hereinafter when taken in conjunction with the drawings which accompany it.